minor #17997 Updated all the README files (javiereguiluz)

This PR was squashed before being merged into the 2.3 branch (closes #17997).

Discussion
----------

Updated all the README files

| Q             | A
| ------------- | ---
| Branch        | 2.3
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Related to #17995.

Commits
-------

2e81248 Updated all the README files

Author: fabpot

README.md

@@ -1,81 +1,14 @@
 DependencyInjection Component
 =============================
 
-DependencyInjection manages your services via a robust and flexible Dependency
-Injection Container.
-
-Here is a simple example that shows how to register services and parameters:
-
-```php
-use Symfony\Component\DependencyInjection\ContainerBuilder;
-use Symfony\Component\DependencyInjection\Reference;
-
-$sc = new ContainerBuilder();
-$sc
-    ->register('foo', '%foo.class%')
-    ->addArgument(new Reference('bar'))
-;
-$sc->setParameter('foo.class', 'Foo');
-
-$sc->get('foo');
-```
-
-Method Calls (Setter Injection):
-
-```php
-$sc = new ContainerBuilder();
-
-$sc
-    ->register('bar', '%bar.class%')
-    ->addMethodCall('setFoo', array(new Reference('foo')))
-;
-$sc->setParameter('bar.class', 'Bar');
-
-$sc->get('bar');
-```
-
-Factory Class:
-
-If your service is retrieved by calling a static method:
-
-```php
-$sc = new ContainerBuilder();
-
-$sc
-    ->register('bar', '%bar.class%')
-    ->setFactoryClass('%bar.class%')
-    ->setFactoryMethod('getInstance')
-    ->addArgument('Aarrg!!!')
-;
-$sc->setParameter('bar.class', 'Bar');
-
-$sc->get('bar');
-```
-
-File Include:
-
-For some services, especially those that are difficult or impossible to
-autoload, you may need the container to include a file before
-instantiating your class.
-
-```php
-$sc = new ContainerBuilder();
-
-$sc
-    ->register('bar', '%bar.class%')
-    ->setFile('/path/to/file')
-    ->addArgument('Aarrg!!!')
-;
-$sc->setParameter('bar.class', 'Bar');
-
-$sc->get('bar');
-```
+The DependencyInjection component allows you to standardize and centralize the
+way objects are constructed in your application.
 
 Resources
 ---------
 
-You can run the unit tests with the following command:
-
-    $ cd path/to/Symfony/Component/DependencyInjection/
-    $ composer install
-    $ phpunit
+  * [Documentation](https://symfony.com/doc/current/components/dependency_injection/index.html)
+  * [Contributing](https://symfony.com/doc/current/contributing/index.html)
+  * [Report issues](https://github.com/symfony/symfony/issues) and
+    [send Pull Requests](https://github.com/symfony/symfony/pulls)
+    in the [main Symfony repository](https://github.com/symfony/symfony)